Transcript of "Bedside monitoring of tissue perfusion and oxygenation"

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Oxygen transport involves a series of convective and diffusive processes. Convective transport-bulk movement of oxygen in air or blood-active, energy consuming processes generating flow Diffusive transport- passive movement of oxygen down its concentration gradient across tissue barriers- across the extracellular matrix- depends on the oxygen tension gradient and the diffusion distance

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Capillary blood to individual cells resting extraction ratio from capillary blood is about 25% may increase to 70­80% during exercise Factors affecting O2 extraction from cappilary blood1. Rate of O2 delivery to capillary2. O2-Hb dissociation relation3. Size of capillary to cellular PO2 relation4. Diffusion distance to cells5. Rate of use of O2 by cells

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Noninvasive measurements of arterial pressure can be determined either manually or by oscillometric method . Oscillometric devices, determine MAP and then provide readings for systolic and diastolic pressures. Oscillometric devices tend to underestimate systolic and overestimate diastolic blood pressure noninvasive measurements less reliable with marked hypovolemia or abnormal cardiac function. Oscillometric measurements also limited by cycling delay of the device.

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Arterial CatheterisationINDICATIONS ABSOLUTE- As a guide to synchronization of intra-aortic balloon counter pulsation PROBABLE-1. Guide to management of potent vasodilator drug infusions2. Guide to management of potent vasopressor drug infusion3. As a port for the rapid and repetitive sampling4. As a monitor of cardiovascular deterioration in patients

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Limitations of CVP Being wrongly used as a parameter/ goal for replacement of intravascular volume The validity as index of RV preload nonexistent Poor correlation with cardiac index, stroke volume, left ventricular end-diastolic volume, and right ventricular end-diastolic volume

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Pulse OximetryAPPLICATIONS indicated in circumstance where hypoxaemia May occur. should be included in the routine vital signs. . continuous monitoring. pattern of oxygenation can be recorded. can replace arterial blood gas analysis in cases where assessment of oxygenation is indication. Regulation of oxygen therapy Testing adequecy of circulation

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Pulse Oximetry Improving oximeter signals• Warm and rub the skin• Apply a topical vasodilator• Try a different probe site, especially the ear• Try a different probe• Avoid motion artefact• Use a different machine

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Monitoring ventilation using end- tidal carbon dioxide provides information regarding alveolar ventilation. PetCO2 - concentration of carbon dioxide at end expiration . measured in both mechanically ventilated and spontaneously breathing patients. displayed as either numerical value (capnometry) or as a graphic waveform plotted against time (capnography). PetCO2 underestimatesPaCO2 by 2 to 5 mm Hg because of the influence of dead space ventilation relationship between PetCO2 and PaCO2 is unreliable in critically ill patients.

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End Tidal CO2 Capnography can be used to monitor patients in whom hypercarbia may be detrimental PetCO2 values greater than 40 mm Hg correlate with equal or higher value of PaCO2 Elevated PetCo2 indicate sthe need for alterations in management

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ScvO2 venous oxygen saturation near the junction of the superior vena cava and right atrium. obtained from subclavian or internal jugular central venous catheter. Because ScvO2 neglects venous return from the lowerbody, values for ScvO2 typically are 3% to 5% less than SvO2 values < 65% -ongoing oxidative impairment. values > 80% - cellular dysfunction with impaired oxygen consumption. - seen in late stages of shock To be used in context with other markers of tissue perfusion (eg, lactate).

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Gastric Tonometry Offers an index of aerobic metabolism in gut mucosa. Based on increase in tissue CO2 A balloon in stomach,measures intramucosal pCO2 Using this and arterial (HCO3), gastric intramucosal PH is calculated

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Near-infrared spectroscopy measures the concentrations of hemoglobin, oxygen saturation,and cytochrome aa3 Cytochrome aa3- final receptor in the electron transport chain - responsible for 90% cellular O2 consumption - remains in a reduced state during hypoxia used primarily to evaluate the perfusion of skeletal muscles.PROBLEMS-signal contamination by light scatter-variable interpretations of the data-lack of a reference standard for comparison

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Near infrared spectroscopy monitoring of transmittance across the brain at two or more wavelengths optical attenuation of the spectra converted into changes of cerebral oxygenation methods include time-resolved, spatially resolved, and phase-resolved spectroscopy INVOS system provides a numerical value for oxygen saturation using rSO2 normal range-60-80% NIRO oximeters present values for oxygenated and total Hb concentration, cytochrome aa3, and a tissue oxyge index

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NISAPPLICATIONS detection of changes during carotid cross-clamping during carotid endarterectomy & cardiac surgery to detect cerebral vasospasm causing delayed cerebral ischemic deficit after SAH assessment of perfusion reductions in stroke Reconstruction of a three-dimensional image using optical tomography attractive because applied by attaching pads to the forehead or other regions of interest.

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Cerebral Microdialysis bedside monitor to provide on-line analysis of brain tissue biochemistry during neurointensive care. The principles and clinical double-lumen probe, lined at it tip with dialysis membrane. perfused by an inlet tube with fluid isotonic to the tissue interstitium perfusate passes along the membrane before exiting collecting chamber. catheter acts as an artificial blood capillary. Measures microdialysate concentrations of glucose, lactate, pyruvate, glycerol, and glutamateThe concentration of these substances in the microdialysate does not correspond to their true extracellular fluid concentration proportion of the extracellular fluid concentration the ‘‘relative recovery”